1. Field of the Invention
The present invention relates to an imaging device in which pixels containing luminance information are arranged.
2. Description of the Related Art
In an image sensor, represented by an image sensor having RGB primary color Bayer layout of related art (see JP-A-2001-218073, for example), when the amplitude of a signal level is small, noise, such as dark current, significantly affects the image quality. Noise reduction may be therefore essential, which however provides a limited effect because of inevitable reduction in the amount of signal due to color filters.
Consequently, there is a need for a noise reduction method for an image sensor in which white (W) pixels are disposed and the layout is inclined 45° to a square.
For example, in a pixel layout used in related art that does not contain W (white) pixels, such as a primary color Bayer layout and a complementary color checkerboard layout, different pixels are used in contour judgment according to whether the portion to be imaged is colored (chromatic color) or not colored (achromatic color), even for subjects having the same luminance. In many cases, there have been devised signal processing in which edge detection, correlation detection and the like is carried out with reference to pixels having “green” components that are primarily responsible for the visual sensitivity characteristic. However, when the subject contains no green signal component or the ratio of the green signal component is low, the performance is significantly degraded or the signal processing itself will not work.
On the other hand, a pixel layout containing W pixels has a high component ratio of W pixels, that is, the number of W pixels is the same as those of color pixels (two to four times the number of each of individual colors that have undergone color separation), and provides a detection signal with a small amount of noise components, so that such a pixel layout is suitable for edge detection, correlation detection and the like. In contrast, the number of pixels that can be used to judge colors is small, causing a problem of difficulty in color reproduction.